THE PHYSIOLOGY OF CELL-DIVISION Bet: 
general biological conception of an essentially bipolar organiza- 
tion in dividing cells so as to include the physico-chemical prop- 
erties of the plasma-membrane. The increase in permeability 
must be sufficiently rapid and marked to produce a consider- 
able fall in the potential-difference across the surface. On 
account of the interdependence of the two potential-differences 
at nuclear and plasma-membranes, a similar fall of potential 
must occur at the nuclear membrane. The latter change produces 
an increase in permeability®! and is possibly responsible for the 
Fig.3 In this figure the probable position and orientation of the gradients at 
the metaphase stage are indicated. The general disposition of the radiations is 
like that seen in the living sea-urchin egg. The + and — signs indicate the re- 
gions of highest and lowest potential in the several fields. The dotted lines repre- 
sent electrical lines of force, corresponding to the paths of the diffusing ions. 
Several negative signs are crowded into the centers to indicate that the current 
density would be greatest there. The membrane over the equatorial regionis 
supposed as yet to have undergone little or no depolarization. 
dissolution of the membrane which shortly follows. The condi- 
tions are then essentially as represented in fig. 3. 
The peripheral layer of cytoplasm and the central nuclear area 
are, for a time, positive, relatively to the adjoining regions. In 
each hemisphere a potential-gradient will exist between the posi- 
tive areas adjoining the two depolarized membranes and the 
region midway between the two which retains its original nega- 
5t The facts of electrical stimulation, particularly Pfliger’s law of cathodal 
stimulation on the make and anodal on break of the current, indicate that the 
permeability of the plasma membrane depends on its condition of electrical polar- 
ization, and that depolarization, whether partial or complete, involves an increase 
in permeability. The stimulating action of the electrical current depends on this: 
ef. my paper on the general conditions of stimulation in the American Journal 
of Physiology, 1908, vol. 22, pp. 77 to 80. Recently Girard has shown that elec- 
trically polarized membranes are in fact much less permeable to electrolytes than 
the same membranes when unpolarized. (See note 49.) 
